Inhibiting the corrosion or rusting of ferrous and non-ferrous metals due to exposure to moisture, air, especially moist air, and chemicals, such as sodium chloride, has been the focus of many proposed coating compositions. Coating compositions are particularly useful for preventing corrosion and rust on chassis components such as frames, crossmembers and engine cradles and other heavy metal parts of automobiles and other transportation vehicles. While, in most cases, ferrous metals, such as iron and steel represent the areas where rust and corrosion problems are particularly encountered, various non-ferrous metals, such as aluminum, are also subject to corrosion.
The corrosion inhibiting compositions which have been or are currently being commercially used, fall generally into two classes. One class of compositions forms thermoplastic, wax-like films which are soft and may be readily stripped off or removed from the metal surfaces, for example, by organic solvent. Furthermore, because these compositions are generally non-drying and lacking in cohesive strength, they can be readily removed by abrasion, impact or elevated temperatures. Significant problems associated with these compositions include low sag resistance during the service life of the vehicle. The use of catalytic converters in many of today's automotive engines results in higher engine operating temperatures. Instances have occurred where the corrosion inhibiting coating has melted and run off metal parts due to high engine temperatures, decreasing the rust prevention value of the coating, and sometimes even causing fires within the engine compartment or under the vehicle.
The other class of compositions is generally epoxy-based, deposited by electro-deposition techniques and cured in paint bake ovens to form hard coatings. These coatings are essentially permanent and are removable only with great difficulty. A problem associated with these compositions for use on frame components is the high overall costs compared to thermoplastic, wax-like coatings. Contributing to the high costs are high capital expense, a greater degree of surface preparation, and high coating and waste disposal costs. Additionally, the electro-deposited coatings do not effectively coat the inside hollow box sections found in many modern automotive frames.
There is a need for a corrosion inhibiting coating which forms a thermoplastic and wax-like film that can withstand long-term, high temperature engine operation without melting off the coated parts, not only to maintain protection to the part, but also to avoid a fire hazard.
U.S. Patent No. 4,094,801, issued Jun. 13, 1978 to Forsberg, discloses a magnesium-containing composition comprising a mixture of at least one magnesium hydroxide, magnesium oxide, or a magnesium alkoxide; at least one oleophilic organic reagent, such as sulfonic and carboxylic acids; water, and at least one organic solubilizing agent for the oleophilic organic reagent. Uses for this composition are said to include as additives for lubricants and fuels and as protective coating compositions for metal surfaces.
U.S. Pat. No. 4,322,479, issued Mar. 30, 1982, to Forsberg, a divisional of a continuation of a divisional of U.S. Pat. No. 4,094,801, discloses a thixotropic magnesium-containing composition comprising at least one of magnesium hydroxide, magnesium oxide, hydrated magnesium oxide, and a magnesium alkoxide; at least one oleophilic organic reagent, such as a carboxylic or sulfonic acid; water, optional under certain conditions; and, at least one organic solubilizing agent for the oleophilic organic reagent. The composition is said to be useful as an additive for lubricants and fuels and as a protective coating or metal surfaces.
U.S. Pat. No. 4,150,192, issued Apr. 17, 1979 to Downey, discloses a sprayable hot melt rust inhibitor composition comprising a mixture of a sulfonate, optionally a carbonate, optionally an oxidized petrolatum, diluent oil, microcrystalline wax, active filler and thermoplastic resin. Uses for this composition are said to be for coating automobile parts.
U.S. Pat. No. 4,386,173, issued May 31, 1983 to Chang discloses a sprayable hot melt coating composition comprising an epoxy resin-elastomer adduct mixture, microcrystalline wax, a petroleum sulfonate complex dispersed in an oil, and other optional ingredients including fillers, pigments and/or additional nonvolatile oil. The petroleum sulfonate complex is admixed with the epoxy resin-elastomer adduct to form a homogenous composition without the use of organic solvents. Uses for this composition are said to be for corrosion prevention.
U.S. Pat. No. 4,729,791, issued Mar. 8, 1988 to Laura et al., discloses a corrosion inhibiting composition containing a thixotropic overbased alkaline earth metal sulfonate complexed with an alkaline earth metal sulfonate, a drying oil, a drier and other ingredients such as mineral oil, waxes, petrolatum and resins. Uses for this composition are said to be for inhibition of corrosion or rusting of ferrous and non-ferrous metals. Drying oils are typically designed to react with oxygen and crosslink to form a film. Disadvantages to drying oils include, typically the presence of organic solvents, a long drying time (4-24 hours) and overspray and drippings which are not reusable. Furthermore, drying oils can cause the coating to buildup on equipment during the application procedure, which must be removed, adding extra labor and time costs to the process.
New corrosion preventative compositions have now been found which incorporate thermoplastic elastomers in an amount effective to impart superior flexibility and adhesion at low temperatures while also imparting superior handling characteristics at high temperatures. Other advantages include stability from separation during long-term storage, lower volatility resulting in a significant reduction in VOC emissions, a high flash point for improved safety during application and use, resistance to water abrasion, and an absence of heavy metals. Furthermore, the present compositions are more cost effective than currently available products, are easier to apply, have a lower density, thus a lighter weight after application, and result in continuously uniform coating thicknesses, regardless of thickness or shape of the metal substrate. These characteristics overcome the deficiencies of previously known compositions, while meeting the strict performance requirements for corrosion resistant coatings used by the automotive industry.